Authoritative rendering; "schema" usage (3.1.1 port of 3927)

This adds a note about the authoritative HTML rendering and adds
a definition for "Schema" to explain the three ways the term
is used in or with the specification.

Author: handrews

versions/3.1.1.md

@@ -14,7 +14,7 @@ An OpenAPI description can then be used by documentation generation tools to dis
 
 For examples of OpenAPI usage and additional documentation, please visit [learn.openapis.org](https://learn.openapis.org/).
 
-For extension registries and other specifications published by the OpenAPI Initiative, please visit [spec.openapis.org](https://spec.openapis.org/)
+For extension registries and other specifications published by the OpenAPI Initiative, as well as the authoritative rendering of this specification, please visit [spec.openapis.org](https://spec.openapis.org/).
 
 ## Table of Contents
 <!-- TOC depthFrom:1 depthTo:3 withLinks:1 updateOnSave:1 orderedList:0 -->
@@ -75,6 +75,12 @@ For extension registries and other specifications published by the OpenAPI Initi
 ##### <a name="oasDocument"></a>OpenAPI Description
 An OpenAPI Description (OAD) formally describes the surface of an API and its semantics. It is composed of an [entry document](#documentStructure) and any/all of its referenced documents. An OAD uses and conforms to the OpenAPI Specification, and MUST contain at least one [paths](#pathsObject) field, [components](#oasComponents) field, or [webhooks](#oasWebhooks) field.
 
+##### <a name="definitionsSchema"></a>Schema
+
+A "schema" is a formal description of syntax and structure.
+This document serves as the [schema](#schema) for the OpenAPI Specification format; a non-authoritative JSON Schema based on this document is also provided on [spec.openapis.org](https://spec.openapis.org) for informational purposes.
+This specification also _uses_ schemas in the form of the [Schema Object](#schemaObject).
+
 ##### <a name="pathTemplating"></a>Path Templating
 Path templating refers to the usage of template expressions, delimited by curly braces (`{}`), to mark a section of a URL path as replaceable using path parameters.
 
@@ -145,7 +151,7 @@ For example, if a field has an array value, the JSON array representation will b
 All field names in the specification are **case sensitive**.
 This includes all fields that are used as keys in a map, except where explicitly noted that keys are **case insensitive**.
 
-The schema exposes two types of fields: Fixed fields, which have a declared name, and Patterned fields, which declare a regex pattern for the field name.
+The [schema](#schema) exposes two types of fields: Fixed fields, which have a declared name, and Patterned fields, which declare a regex pattern for the field name.
 
 Patterned fields MUST have unique names within the containing object.